This invention relates to a novel light emitting diode (LED) and techniques for mounting such an LED on a substrate. A method for manipulating the LEDs is also provided.
Light emitting diodes have become extremely popular with many millions of them manufactured annually. There is a continuing effort to make smaller LEDs since the smaller they can be made, the larger the number of LEDs produced from a semiconductor wafer. This can effect an appreciable cost reduction. A principal limiting factor in reducing the size of LEDs has become the electrical connections.
Typically, an LED is mounted with one electrode on a conductive substrate such as a printed circuit board, a wire leadframe or the like, with the light emitting junction parallel to the substrate. A very small wire is then "wire bonded" or welded to a small metallized area on the top face of the LED. The metallized area needs to cover less than the entire top surface so that light can be radiated from the LED. About the smallest dimensions suitable are 250 micrometer cubes.
Tape automated bonding is sometimes used to replace wire bonding since techniques have been developed for simultaneously bonding many different bond pads, instead of one at a time as with conventional wire bonding. Gang tape automated bonding, however, requires excellent coplanarity of all of the bond pads and is inappropriate for bonding a matrix of LEDs simultaneously. Furthermore, the smallest LEDs suitable for tape automated bonding are about 200 micrometer cubes. The equipment for either tape automated bonding or wire bonding is quite costly.
What is needed is a totally different approach to mounting an LED, making electrical contact with an LED, methods for handling such LEDs, and substrates for receiving such LEDs.